1. Field of the Invention
This invention relates to electrophotographic photosensitive members and more particularly to an electrophotographic photosensitive member having a photosensitive layer containing a novel organic photoconductive material selected from a series of hydrazone compounds.
2. Description of the Prior Art
There have so far been known inorganic photoconductive materials such as selenium, cadmium sulfide, zinc oxide, etc. as photoconductive materials used for electrophotographic photosensitive members. In contrast to their many advantages, for instance, chargeability to a suitable potential in a dark place, slight dissipation in a dark place, and capability of dissipating rapidly charge by light irradiation, these photoconductive materials have various disadvantages, for example, as follows: in the case of selenium type photosensitive members, the crystallization of the photoconductive materials readily proceeds under the influence of surrounding factors such as temperature, moisture, dust, and pressure, in particular remarkably when the surrounding temperature exceeds 40.degree. C., thus resulting in lowering of chargeability or white spots in image. In the case of these photosensitive members and cadmium sulfide type photosensitive members, stable sensitivity and durability cannot be obtained in repeated operations under high humidity conditions. In the case of zinc oxide type photosensitive members, which require sensitization by a sensitizing pigment, Rose Bengal being a typical sensitizing pigment, stable images over a long period of time cannot be obtained, since the sensitizing pigment tends to cause charge deterioration by corona discharge and light fading by exposure to light.
On the other hand, various kinds of organic photoconductive polymers have been proposed the first of which was polyvinylcarbozole. However, although excellent in film forming properly, in lightness, and in some other points as compared with said inorganic photoconductive materials, these polymers have until now failed to be put to practical use, by reason that they are still unsatisfactory in film forming property and inferior to the inorganic photoconductive materials in sensitivity, durability, and stability to changes in environmental conditions.
There have been also proposed low-molecular organic photoconductive materials such as hydrazone compounds disclosed in U.S. Pat. No. 4,150,987, triarylpyrazoline compounds in U.S. Pat. No. 3,837,851, 9-styrylanthracene compounds in Japanese Patent Kokai Nos. 94828/1976 and 94829/1976, and 4-chlorooxazole compounds in Japanese Patent Kokai No. 53278/1980. These low-molecular organic photoconductive materials are unsatisfactory in sensitivity, although it has become possible by proper selection of a binder used to eliminate therefrom the disadvantage of lacking the film-forming property, which has been a problem in organic photoconductive polymers.